1. Field of the Invention
The present invention relates to a subscriber data control method in a mobile communication network, and more particularly to a subscriber data control method in a mobile switching center when a visitor mobile station has entered into a service area controlled by the mobile switching center.
2. Description of the Related Art
The mobile communication network is constituted by a plurality of mobile switching centers as the backbone nodes of a communication network and a plurality of base stations which are controlled by the mobile switching centers and providing radio communication areas (cells). In the actual mobile communication network, a base station control unit that controls the base stations exists between each mobile switching center and each base station, but the technique related to the present invention is not directly involved in the existence of the base station control unit. Accordingly, a description is made assuming that the base station control unit is contained in the mobile switching center.
When a person is newly registered as a mobile communication subscriber (hereinafter referred to as “mobile station”) with respect to a mobile communication network provider that managers the above-mentioned mobile communication network, subscriber data relating to the mobile station is registered in a mobile switching center that handles a service area in which the mobile station is normally used. The subscriber data includes various data given to each mobile station individually, and is made up of the representative data, a subscriber number allocated to the mobile station, an equipment number of the mobile station, the contents of service subscribed, registered location information, and so on.
Also, as described above, the mobile switching center is a backbone node of the mobile communication network, and controls a plurality of base stations which provide a plurality of radio communication areas (i.e., cells) as a service area. Therefore, there are a plurality of service areas in the mobile communication network, and each of the service areas are managed and controlled by the respective mobile switching centers. With respect to a particular mobile station, a mobile switching center, in which subscriber data of the mobile station is registered, is called as a home mobile switching center, and a service area controlled by the home mobile switching center is called a home service area. On the other hand, a mobile station, which is located in a particular service area and its subscriber data is not registered in a mobile switching center managing the service area, is called a visitor mobile station to the mobile switching center.
When a mobile station has moved from one service area to another service area, the mobile station is informed that it has moved to a different service area by broadcasting information transmitted in respective service areas. Then, the mobile station performs a location registration operation to notify the mobile communication network that the mobile station has changed the locating service area.
FIG. 1 is a block diagram for explaining a control operation when the mobile station moves around the mobile communication network. The structure of the figure will be described.
Mobile switching centers (MSCs) 1 to 3 constitute a service area H, a service area A and a service area B by base stations (BSs) 11 to 1n, 21 to 2n and 31 to 3n, respectively. A mobile station (MS) 4, its subscriber data has been registered in the MSC 1, is moving through respective service areas. As described above, the MSC 1 is called “home switching center” to the MS4 because the subscriber data of the MS 4 is registered in the MSC 1, and also the service area H is called “home service area”. On the contrary, since the MSCs 2 and 3 are mobile switching centers to which the MS4 is going to visit, respectively, they are called “destination A MSC” and “destination B MSC” to MS4.
In the mobile communication network thus structured, the control operation in the case where the MS4 has moved from the service area H to the service area A will be described.
Upon entering the service area A, the MS4 receives a location registration area number announced by the base stations constituting the service area A and discriminates that the location registration area number is not identical with that stored in the self mobile station. As a result, the MS4 knows that it has moved to a new location registration area (=a service area), and renews the location registration area stored in the self mobile station for a new location registration area number, and notifies the mobile communication network that it has moved to a different service area by transmitting a location registration signal.
The MSC 2 of the service area A, which has received a notification of the location registration by the location registration signal transmitted from the MS 4 through one of base stations in the service area A, performs the location registration request operation for the MS 4. The MSC 2 requests the MSC 1, which is the home MSC of the MS 4 and discriminated by a equipment number transmitted with the location registration signal, to register a new location of the MS 4 (i.e. service area A), and also request the MSC 1 to transfer the subscriber data relating to the MS 4. Then, the MSC 1 renews the location registration information of the MS 4 registered in the subscriber data, and transfers the subscriber data relating to the MS 4 to the MSC 2. The MSC 2 registers the subscriber data of the MS 4 transferred from the MSC 1 as visitor subscriber data in a subscriber data storage area of visitor subscribers.
A call to be terminated to the MS 4, which is visiting to other service area, is first routed by the MSC 1 which is a home MSC of the MS 4, and it is discriminated that the MS 4 exists in the service area A by referring to the location registration information stored in the MSC 1. Then, the call is routed to the MSC 2. The MSC 2 refers to the subscriber data stored in the subscriber data storage area of visitor subscribers, and instructs base stations in the service area A to transmit a paging signal for the MS 4. As the equipment number of the MS 4 is designated in the paging signal, the MS 4 replies to the paging signal when the equipment number of the MS 4 coincides with the equipment number designated in the paging signal, and then, the call is terminated to the MS 4 which has responded to the paging signal.
Also, in the case of dealing with a call origination of the MS 4 by the MSC 2, the MSC 2 refers to the subscriber data in response to the call request from the MS 4, and performs a call origination control in accordance with the subscriber data of the MS 4.
When the MS 4 further moves, and is entering the service area B, the MS 4 transmits the location registration signal in the same manner as the operation performed at the service area A. As the result, the MSC 3 requests the MSC 1 to register new location of the MS 4 (service area B) and to transfer the subscriber data of the MS 4. The MSC 1 responds to the request, and transmits the subscriber data of the MS 4 to the MSC 3. When the MSC 1 knows that the service area in which the MS 4 exists has been changed, the MSC 1 transmits a subscriber data delete request to the MSC 2 to delete the subscriber data of the MS 4 which is no longer required in the service area A. The MSC 2, which has received the subscriber data delete request, deletes the subscriber data of the MS 4 stored as the visitor subscriber data, and sends a delete response back to the MSC 1.
As described above, in the mobile communication system, with the movement of the mobile station, the subscriber data transfer request and the subscriber data delete request are frequently transferred between mobile switching centers, and also the subscriber data registration operation and the subscriber data delete operation are similarly frequently performed in each mobile switching center.
Subsequently, referring to FIG. 2, the tendency of the service area structure in the mobile communication network will be described.
The service area structure in a large city area tends to form concentric circulars by each service area as shown in FIG. 2(A). This aims for expecting such an effect that traffic in each of the service areas is dispersed more as compared with the service area structure forming the wide stretch in the X-Y axial directions as shown in FIG. 2(B).
For example, it is assumed that the down towns exist at positions shown in the figure. Since it is presumed that the mobile station moves along the down town, in case of the service area structure of FIG. 2(B), it tends to occur a condition that the traffic is concentrated in the service area 2 and the service area 4 but there is few traffic in the service area 1 and the service area 3. On the contrary, in case of the service area structure of FIG. 2(A), the occurring traffic is dispersed in the respective service areas 1, 2 and 3. This dispersion of the traffic is desirable because it is effective from the viewpoint of an equipment plan in the mobile communication network.
In the control operation of the mobile communication switching center, an internal processing load relating to the control operation to be performed for the movement of the mobile station is as same amount as or larger than that of the control operation for handling to a call as compared with the switching center of a fixed communication network.
In particular, in the mobile communication network in which the concentric circular service areas are disposed as shown in FIG. 2(A), because the movement of the mobile stations which crosses from one service area to another service areas is severely increased, the registration and the deletion for the visitor subscriber data are frequently carried out, and the number of control signals for the registration request and the deletion request is increased. In addition, in the case where the mobile station existing in the vicinity of the boundary of the service area moves unsteadily, the location registrations are frequently carried out at relatively short time intervals until the mobile station finally enters any one of the service areas.
This results in that an unnecessary load is applied to the mobile switching center because the above-described registration process and the deleting process for the visitor subscriber data are frequently carried out. Especially under the heavy traffic condition, the load of such internal processing affects a call connection processing, which is inherently performed by the mobile switching center, and resulting in such a problem that the call connection processing is suspended in the worst case.
Also, the mobile station belonging to another service area seems to be existing in the visiting service area as far as it has performed the location registration in the visiting service area, and the subscriber data of the mobile station transmitted from the home switching center is always held in the memory area for the visitor mobile station until receiving a deleting request from the home switching center.
In the case where a user of the mobile station in the visiting service area turns off the power of the mobile station and has moved to another service area, or a user of the mobile station in the visiting service area goes to an underground area, where no radio signal is received, and has moved to another place by a subway, the visitor subscriber date of those mobile stations held in the mobile switching center are no longer necessary. The visitor subscriber data of such mobile stations are held until the home switching center receives the location registration request of the mobile station from another mobile switching center and recognizes that the mobile station has moved to another service area, and this results in such a problem that the memory area for the visitor subscriber data is used in vain.